Ring laser gyroscopes are commonly used as angular rate sensors. An integral part of the ring laser gyro is the laser beam source or generator. One form of a laser beam generator comprises a gas discharge device. The gas discharge device is used to create a light beam. This light beam is then transmitted around a closed-loop path. A plurality of cavities in combination with a plurality of mirrors define the closed path. The path is usually triangular or rectangular, but any closed-loop polygonal path could also be used.
Present day gas discharge devices use a He-Ne gas which is excited by an electric current passing therethrough, consequently ionizing the gas and creating a plasma. As is well understood by those skilled in the art, the ionized gas produces a population inversion which results in the emission of photons, and in the case of He-Ne generation of a visible light. The He-Ne gas is contained within the aforementioned closed-loop path. By exciting the gas within the closed-loop path, the emitted visible light is forced to propagate around the closed-loop path. Two counterpropagating light signals are created, each traveling around the close-loop path in opposite directions.
It should be noted that prior art ring laser gyro systems are usually provided with a pair of electrical currents which flow in opposite directions. Each of the electrical currents create plasma in the gas. The current is established by applying electrical potential, of sufficient magnitude, between one cathode and one anode. As a consequence of the electrical current passing through the gas the gas molecule flow is affected. Since the electrical currents usually flow in at least a portion of the path traversed by the laser beams, the gas molecule flow caused by the electrical current results in a bias or error term in the gyro output. Accordingly, in the field of ring laser gyros, a pair of electrical currents are usually generated in order to balance the gas molecule flow effects caused by the individual currents. In ring laser systems of the prior art, a pair of electrical currents can be provided by a single cathode and a pair of anodes symmetrically placed relative to the closed-loop path of the laser beams. This configuration results in the gas flow effects caused by one of the electrical currents to be balanced by gas flow effects caused by the other one of the electrical currents.
Ring laser gyro systems similar to that just described have two inherent characteristics which hinder the ability to make the device lase. First, the body forming the optical cavity is usually of a very high dielectric index material causing the existence of stray capacitance between the electrodes and other parts of the structure. This stray capacitance causes an electrical charge to build up on or in the cavity, creating an electric potential which must be overcome to initiate electrical current between the cathode and anode.
Further, in some systems, particularly triangular ring lasers, the electrodes are not in a straight line relationship with each other through the cavities Current traveling through the gas between the cathode and anode must follow through at least a pair of connected cavity line segments forming the closed-loop path. This configuration requires the discharge current to travel around a corner. As a result, the start up potential required to initiate the electrical currents between each cathode and anode pair is very large and much greater than that required to initiate a current through a straight tube laser.
This type of arrangement where the cathode and the anodes are not in straight line relationship is illustrated in FIG. 1. There is shown a gyro block 110 having a plurality of interconnecting tunnels 12, 14 and 16. Attached to block 110 are a plurality of mirrors 20 which reflect light beams through interconnecting tunnels 12, 14 and 16. The mirrors also enclose the tunnels 12, 14 and 16, forming a closed-loop cavity.
Attached to block 110, on a first side 112, is a cathode 130. Cathode 130 communicates with the closed-loop cavity via a communication port 132 Also attached to block 110 is a first anode 140 and a second anode 142 which are attached to a second side 114 and a third side 116, respectively. First anode 140 and second anode 142 communicate with the closed-loop cavity via communication ports 134 and 136, respectively.
To initiate the flow of a discharge current a very large potential must be applied between the cathode 130 and the first anode 140, as well as between the cathode 130 and the second anode 142. As can be seen, the discharge current is required to flow around a corner (see a first corner 150 and a second corner 152), thus a very large starting potential is required between cathode 130 and the anodes 140 and 142.
In the prior art, initiation of electrical currents between the cathode and anode to cause ionization of the gas and subsequently cause the generation of laser beams is unreliable, usually slow to start, and requires a very large start up electrical potential between each cathode and anode pair.